U.S. Pat. No. 3,987,403 issued Oct. 19, 1976 for "Sensory Aids For The Blind" describes an electronic audio aid in which a frequency swept ultrasonic carrier signal is generated and radiated as acoustic energy from a headset. Reflected acoustic energy is received by two spaced-apart receiving transducers which feed a two channel receiver. The two receiving transducers have divergent polar lobes which in combination with the polar lobe of the transmitting transducer simulate the characteristics of a normal human auditory system. The carrier signal is multiplied with each received signal to produce respective beat frequency signals each of which have a frequency and level which is dependent upon the range and direction respectively of the target source of reflection which respect to the user. The gain of both channels is controlled synchronously by controlling the level of the carrier signal multiplied with each received signal. Range of gain control can be increased by feeding the transmitting transducer with the control level carrier signal.
The sensory system described in U.S. Pat. No. 3,987,403 operates with an ultrasonic carrier and requires a separate transmitting transducer and two separate receiving transducers (one for each ear) in addition to the ultrasonic carrier signal generating circuit for the transmitter and reflected ultrasonic signals returned from the target which must be processed in a receiving channel for each ear, in addition to the converting circuitry for converting the reflected and returned ultrasonic signals in each receiving channel to the audible range in order to be perceived by the user. Thus, the audio aid described in this patent is quite complex and costly, requiring a large number of interrelated parts and components and is difficult to maintain in alignment during operation, thus requiring considerable skill on the part of the user. To overcome these objectional features found in currently available audio aids for the blind, the present invention was devised.